It is known that a semiconductor device, for example, an EPROM device, has a surface passivation film, usually consisting of a phosphosilicate glass (PSG), on the uppermost surface of the EPROM device in order to protect the EPROM device from alkaline ions and moisture. On the other hand, a silicon nitride (Si.sub.3 N.sub.4) film formed by a plasma vapor phase growth method is finding use as a surface passivation film for semiconductor elements, because silicon nitride is superior in moisture proofness to PSG. However, the silicon nitride has an absorption edge at a wave length of about 2800 .ANG., which causes the silicon nitride to be impermeable to ultraviolet rays. Accordingly, the silicon nitride film is not usable as a surface passivation film for an EPROM device whose memory is to be erased by ultraviolet rays having a central wave length of 2537 .ANG..